7,187 research outputs found
Representation theory for vector electromagnetic beams
A representation theory of finite electromagnetic beams in free space is
formulated by factorizing the field vector of the plane-wave component into a
mapping matrix and a 2-component Jones-like vector. The mapping
matrix has one degree of freedom that can be described by the azimuthal angle
of a fixed unit vector with respect to the wave vector. This degree of freedom
allows us to find out such a beam solution in which every plane-wave component
is specified by the same fixed unit vector and has the same
normalized Jones-like vector. The angle between the fixed unit
vector and the propagation axis acts as a parameter that describes the
vectorial property of the beam. The impact of is investigated on a
beam of angular-spectrum field scalar that is independent of the azimuthal
angle. The field vector in position space is calculated in the first-order
approximation under the paraxial condition. A transverse effect is found that a
beam of elliptically-polarized angular spectrum is displaced from the center in
the direction that is perpendicular to the plane formed by the fixed unit
vector and the propagation axis. The expression of the transverse displacement
is obtained. Its paraxial approximation is also given.Comment: 16 pages. The final version appears in the Phys. Rev.
Electron beams of cylindrically symmetric spin polarization
Cylindrically symmetric electron beams in spin polarization are reported for
the first time. They are shown to be the eigen states of total angular momentum
in the direction. But they are neither the eigen states of spin nor the
eigen states of orbital angular momentum in that direction.Comment: 10 pages and 2 figure
Coronal rain in magnetic bipolar weak fields
We intend to investigate the underlying physics for the coronal rain
phenomenon in a representative bipolar magnetic field, including the formation
and the dynamics of coronal rain blobs. With the MPI-AMRVAC code, we performed
three dimensional radiative magnetohydrodynamic (MHD) simulation with strong
heating localized on footpoints of magnetic loops after a relaxation to quiet
solar atmosphere. Progressive cooling and in-situ condensation starts at the
loop top due to radiative thermal instability. The first large-scale
condensation on the loop top suffers Rayleigh-Taylor instability and becomes
fragmented into smaller blobs. The blobs fall vertically dragging magnetic
loops until they reach low beta regions and start to fall along the loops from
loop top to loop footpoints. A statistic study of the coronal rain blobs finds
that small blobs with masses of less than 10^10 g dominate the population. When
blobs fall to lower regions along the magnetic loops, they are stretched and
develop a non-uniform velocity pattern with an anti-parallel shearing pattern
seen to develop along the central axis of the blobs. Synthetic images of
simulated coronal rain with Solar Dynamics Observatory Atmospheric Imaging
Assembly well resemble real observations presenting dark falling clumps in hot
channels and bright rain blobs in a cool channel. We also find density
inhomogeneities during a coronal rain "shower", which reflects the observed
multi-stranded nature of coronal rain.Comment: 8 figure
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